A non-servo drum brake assembly includes an anchor plate for pivotally mounting adjacent ends of a pair of brake shoes. A hydraulic actuator is engageable with the pair of brake shoes to pivot the same radially outwardly about the anchor plate so as to engage the pair of brake shoes with a rotatable member.
A duo-servo drum brake assembly includes a connecting member, such as an extendible adjuster, between adjacent ends of a pair of brake shoes. The connecting member is a floating member relative to the backing plate so that the pair of brake shoes and connecting member move or rotate with the rotatable member through a slight arcuate angle during braking. This slight arcuate movement of the pair of brake shoes results in one of the pair of brake shoes being biased into engagement with the rotatable member by the slight movement of the other brake shoe. As a result the duo-servo brake is more efficient than the non-servo brake under similar operating conditions.
With the increase in front wheel drive for motor vehicles, disc brakes on the front wheel and drum brakes on the rear wheel are becoming very common. Moreover, the disc brakes on the front wheel are more than adequate to control braking for the motor vehicle so that the drum brakes on the rear wheel are not required to absorb a majority of the kinetic energy of the moving car. In fact, if the rear drum brake is too efficient, a service brake application will cause the rear wheels to lock up, thereby creating a dangerous driving condition. In general, non-servo drum brakes are used on the rear wheels.
Although the non-servo rear drum brake is suitable during a service brake application, because the front disc brake is doing most of the braking, a parking brake application presents a different situation as only the rear brake is utilized. Consequently, a rear drum brake which is designed as a supporting brake during a service brake application is relied on to totally perform braking for a motor vehicle during a parking brake application.